Micro-electromechanical systems (MEMS) are used in a variety of applications, including optical display systems. In many optical display systems, arrays of MEMS devices commonly referred to as pixels are electromechanically controlled to reflect image-carrying modulated light toward display optics for display. As a light source projects light rays onto the pixels, the pixels reflect modulated light rays carrying image data toward the display optics. The pixels may be electromechanically controlled to regulate the characteristics of the modulated light. For example, some pixels include spatial gaps that are controlled to determine the characteristics of the modulated light. For example, the spatial gap may be set to a distance that limits the reflected modulated light to a particular range of wavelengths.
As light rays from the light source reach the pixels, a certain amount of the light rays reflects off of the surfaces of the pixels and mixes with the modulated light. For example, some types of pixels have a partially reflective top plate. The surface of the top plate of such a pixel will reflect a portion of the light rays away from the pixel. Light that reflects off of pixel surfaces is commonly referred to as stray light. If the amount of stray light that mixes with the modulated light is high, the resulting display images will have poor contrast.
Stray light can also be introduced by other surfaces of optical display systems. In particular, any surface positioned between the light source and the pixels may reflect a portion of the light rays away from the pixels. For example, many optical display systems include a cover plate placed over arrays of pixels to protect the pixels from harm. However, like the surfaces of the pixels, the surface of the cover plate tends to produce stray light by reflecting some incident light rays away from the pixels. The light reflected off of the cover plate is also known as stray light and may mix with the modulated light. Consequently, conventional cover plates may degrade the contrast of display images.
One attempt to curtail the effects of stray light reflections from the surfaces of pixels and cover plates includes the use of anti-reflective coating specifications for pixel surfaces and cover plates. Anti-reflective coatings on the surfaces of pixels and cover plates are used to reduce the reflection from these surfaces. However, the residual reflections from the anti-reflection coated surfaces still reduce the contrast in modern high performance projector systems.
An approach for reducing the stray light even further includes superimposing pixel arrays one over another. However, this approach is frequently complicated and expensive to implement. Not only is the cost of parts increased, the superimposed pixel arrays must be positioned and remain in proper alignment with each other for proper operation of the display systems that make use of this approach.